23 Weeks.

Saybie, Born At 8.6 Ounces, Is Now Believed To Be The World's Tiniest Surviving Baby

She was born at a San Diego hospital prematurely at 23 weeks of gestation weighing about as much as a large apple.

https://www.npr.org/2019/05/29/728118503/saybie-born-at-8-6-ounces-in-san-diego-is-now-the-worlds-tiniest-surviving-baby